1. Field of the Invention
The present invention relates to a pneumatic tire having a layer for preventing of air permeation which enables a reduction in the weight of the tire and is superior in bonding with a rubber layer, without detracting from the retention of air pressure in the tire and also relates to a process for the production of the same.
The present invention further relates to a pneumatic tire having a layer for preventing of air permeation which enables a reduction in the weight of the tire, is superior in bonding with the rubber layer, and, in superior in water resistance, heat resistance, and, in some cases, durability etc., without detracting from the retention of air pressure in the tire and also relates to a process for the production of the same.
2. Description of the Related Art
The reduction of fuel consumption is one of the major technical problems to be solved in the automobile industry. There have been increasingly stronger demands for reduction of the weight of the pneumatic tires as part thereof.
The inner surface of a pneumatic tire is provided with an inner liner layer composed of a low gas-permeable rubber such as halogenated butyl rubber so as to enable the tire air pressure to be kept constant. A halogenated butyl rubber, however, suffers from a large hysteresis loss. For this reason, when, after vulcanization of the tire, there are waves formed in the inner surface rubber of the carcass layer and the inner liner layer in the space between the carcass cords, the inner liner rubber layer deforms along with the deformation of the carcass layer. Thus there is the problem that the rolling resistance increases. Therefore, in general, the inner liner layer (e.g., halogenated butyl rubber) and inner surface rubber of the carcass layer are joined through a rubber sheet which is called a tie gum with a small hysteresis loss. Accordingly, in addition to the thickness of the inner liner layer of the halogenated butyl rubber, there is added the thickness of the tie gum and the layer as a whole becomes a thickness of over 1 mm (i.e., 1000 .mu.m). As a result, this becomes one factor increasing the weight of the final tire product.
Various proposals have been made for using various materials, in place of the low gas-permeable rubber such as butyl rubber, as the inner liner layer or other air permeation preventive layer of the pneumatic tire. For example, Japanese Examined Patent Publication (Kokoku) No. 47-31761 discloses the coating of the inner surface of a vulcanized tire from 0.1 mm or less of a solution or dispersion of a synthetic resin such as polyvinylidene chloride, a saturated polyester resin, or a polyamide resin having an air permeation coefficient (cm.sup.3 (standard state)/cm.multidot.sec.multidot.mmHg)) of not more than 1.0.times.10.sup.-12 or less at 30.degree. C. and of 5.0.times.10.sup.-12 or less at 70.degree. C.
The techniques disclosed in this publication provide the inner surface of the carcass of a vulcanized tire or the inner surface of the inner liner with a coating of a synthetic resin having a specific air permeation coefficient and making the thickness of the synthetic resin coating 0.1 mm or less, but the pneumatic tire disclosed in the publication had a problem in the bonding between the rubber and synthetic resin and further had a defect that, when a polyamide resin was used as the inner liner layer, the heat resistance and moisture resistance (or water resistance) were poor. Note that this publication did not disclose the use of an alkoxyalkylated polyamide, multiple copolymer polyamide resin, alkoxyalkylated polyamide, etc.
Several proposals have been made for using a vinylidene chloride resin for an air permeation preventive layer of a pneumatic tire. For example, Japanese Examined Patent Publication (Kokoku) No. 47-31761 proposes a tube-less tire which is coated with a synthetic resin such as a vinylidene chloride resin and discloses a vinylidene chloride-acryl ester copolymer. Further, Japanese Unexamined Patent Publication (Kokai) No. 5-278409 proposes to construct an inner liner layer by coating a thin film or solution of a vinylidene chloride-vinyl chloride copolymer on the inner surface of a tire, followed by vulcanizing. A vinylidene chloride-vinyl chloride copolymer, however, has a Tg of 40.degree. C. or less and is inferior in long term heat resistance, and therefore, is not suitable for long term use at temperatures of, for example, about 80.degree. C. A vinylidene chloride-vinyl chloride copolymer includes a large amount of chlorine, and therefore, easily degrades under heat. Further, most of them include up to 10% by weight of plasticizers for improving the workability or processability, but these plasticizers shift and the film hardens and the physical properties deteriorate. Thus there is the problem that they are not practical.
Japanese Unexamined Patent Publication (Kokai) No. 5-330307 discloses to halogenate the inner surface of the tire (using a conventionally known chlorination solution, bromine solution, or iodine solution) and form on top of that a polymer coating (thickness of 10 to 200 .mu.m) of methoxymethyl nylon, a copolymer nylon, a blend of polyurethane and polyvinylidene chloride, or a blend of polyurethane and polyvinylidene fluoride. This publication, however, discloses the use of an acid catalyst composed of an organic acid such as citric acid or tartaric acid as a cross-linking catalyst for curing the methoxymethylated nylon, but such an acid catalyst causes the problem of an inferior flex fatique due to deterioration after curing and of early cracking during use and it is difficult to say that the bondability is sufficient either. Further, the art disclosed in the publication suffers from the problem of a poor moisture resistance (or water resistance) or heat resistance of the air permeation preventive layer when an uncross-linked or uncured polyamide resin is used, as the inner liner layer due to the non-crosslinking or curing thereof.
Further, Japanese Unexamined Patent Publication (Kokai) No. 5-318618 discloses a pneumatic tire having a thin film of methoxymethylated nylon as an inner liner. According to this proposal, the inner surface of a green tire is sprayed or coated with a solution or emulsion of methoxymethylated nylon, then the tire is vulcanized or alternatively the inner surface of a vulcanized tire is sprayed or coated with a solution or emulsion of methoxymethylated nylon so as to produce a pneumatic tire. However, since there is no treatment for bonding between the rubber of the inner surface of the tire and the methoxymethylated nylon, when the tire is used at a high load, there are still the problem that the methoxymethylated nylon film peels off from the rubber of the inner surface of the tire and the problem that the resistance to humidity (or water resistance) and heat resistance of the inner liner layer are poor due to the fact the methoxymethylated nylon is not cross-linked or cured.